The long-term objective of this proposal is to establish the foundation for a relatively small, inexpensive, but very powerful instrument for obtaining structural information from and molecular weights of high mass biomolecules. Specifically, the instrument will couple electrospray ionization with a quadrupole ion trap mass spectrometer. Electrospray ionization has been shown to be capable of producing highly charged ions from large biomolecules (MW > 104 Da). A quadrupole ion trap can be used to manipulate these ions both to provide molecular weights and to provide structural information. This work is devoted to optimizing the interface between the electrospray on source and the mass analyzer, exploring and optimizing instrumental techniques for mass/charge measurement, and performing fundamental research on the reactivities of the highly charged biomolecules in the ion trap environment. The latter work is designed to maximize both sensitivity and the amount of structural information obtained. This work will benefit the biomedical community by providing relatively low-cost means for making accurate molecular weight determinations and for obtaining structural information from a wide range of high mass molecules. The proposed instrument, due to its small size and low cost, would be much more accessible to researchers in the biomedical community than the much larger and more expensive instrumentation presently available.